Conventionally, in radio communications, to improve reception quality, there are performed an antenna diversity transmission that switches an antenna to transmit the same signal and an automatic repeat request that retransmits a signal according to a request from a receiving side when an error occurs in the signal. However, in the antenna diversity transmission, since multiple antennas must be prepared, an apparatus scale on a transmitting side will be increased. Additionally, in the automatic repeat request, the frequency of retransmission will increase as an error rate is high, resulting in a reduction transmission efficiency.